Polymer Composites with Nanomaterials for Strain Gauging: A Review

Abstract

Strain gauges and strain gauge transducers are important tools in the field of material resistance research to measure the stresses and strains in solids. These methods and devices have a wide range of applications, from construction to mechanical engineering, where the mechanical properties of materials need to be monitored and optimized. The use of nanomaterials in strain gauges allows for more sensitive and compact sensors. Nanotechnology makes it possible to create strain gauges with improved mechanical and electrical properties. At the same time, nanomaterials have unique properties that make them ideal for use in strain gauges. This paper considers different types of composites based on polymer matrices with additives of dispersed nanomaterials, which are designed for strain gauge tasks. Thermoplastics and elastomers can be used as polymer matrices. Dispersed fillers can be based on MXene and nanomaterials such as carbon nanotubes, graphene, metals, etc. Despite the obvious advantages of strain gauges based on conducting polymers modified with dispersed structures, there are problems in creating effective strain gauges with the ability to operate under large deformations with an improved sensitivity and accuracy of measurements in a wide range. This article also provides brief information on the technical evolution of strain gauges, from wire and foil to polymer nanocomposites. A modern classification of strain gauges is provided. The disadvantages and advantages of existing strain gauges are shown. The review contains information on commercial strain gauges. The mechanisms of electrical conductivity formation in polymer composites for strain gauges are described in detail. The areas of application of polymer nanocomposite strain gauges are also specified in detail. The purpose of this review study is to determine the prospects for the use of various nanomaterials as additives in polymers to create strain gauges. The review is aimed at a wide range of readers.

1. Introduction

As the complexity of the structures and materials used in modern engineering increases, so does the need for more accurate and reliable methods for stress and strain monitoring. Strain gauges, in turn, are used to measure the force or strain on the surface of an object.

The measurement of pressure and associated deformation and mechanical stresses acting on different types of surfaces of parts or devices is relevant in a wide range of technological and scientific and technical tasks [1]. Traditional and classical devices for strain gauge measurements may be insufficiently accurate or inconvenient for application in certain situations. The accuracy of the strain gauge depends on the environmental conditions. Therefore, in the lower and upper parts of the strain gauge operating range, compensation is required. Standard models operate correctly at temperatures from −40 to +65 °C. However, there are strain gauges for special operating conditions, which will also be discussed in this article.

This creates the need to develop more effective and convenient technical solutions for strain gauge tasks. The ability to measure mechanical deformations such as tension, torsion, and compression is required in portable electronic devices [2], soft robotics [3], human motion parameter detection [4], virtual reality technology [5], human health monitoring [6], rock fracture research [7], the strain gauging of car parts [8], mechanical engineering technology [9], aviation technology [10], and other various technical applications [11,12,13,14]. A strain gauge, or strain resistor (from Latin tensus—“tense”), is a load meter used in devices for determining the mass of a load (Figure 1).

Strain gauges are of a high relevance for measurement technology, control, and management systems [15]. The main sensitive element of strain gauges is a primary measuring transducer that generates an electrical signal under mechanical deformation.

In 1843, S. Wheatstone described the effect of resistance changes in an electric conductor under the action of mechanical strain. In 1938, E.E. Simons and A.C. Ruge invented, almost simultaneously, but independently, the strain gauge. In 1952, the “metal foil strain gauge” method was mentioned for the first time [16,17,18].

A strain gauge is defined as a change in the specific electrical resistance of a material caused by mechanical deformation [19]. Thus, a strain gauge is a resistor whose electrical resistance changes depending on its deformation. This follows, in particular, from the well-known formula for the electrical resistance of a conductor, as follows:

(1)$R=\rho {\displaystyle \frac{l}{S}},$

where R is the resistance of the conductor, ohm; l is the length, m; S is the cross-sectional area of the conductor, m²; and ρ is the proportionality coefficient depending on the conductor material or specific resistance, (ohm∙m²)/m.

Formula (1) shows that, when a conductor included in an electric circuit is deformed, its geometric parameters l and S change, hence, so does its electrical resistance. A change in the electrical resistance of the conductor leads to a change in the electric current flowing in the circuit, which can be recorded by an electrical measuring device, including the use of a bridge circuit. At the same time, the specific resistance changes, which also depends on temperature.

A wire resistance sensor (Figure 2) is shown as an example, with the so-called loop winding of the wire [20]. This sensor is based on thin paper (2), to which the sensor wire is glued, arranged in the form of several identical loops, forming the wire grid (1) of the sensor. To the ends of the sensor, wire lattices are connected by soldering or welding leads (3) made of copper wire or foil, which are used to connect the sensor to the measuring equipment. The wire grid of the sensor is usually sealed with another protective layer on top.

Nowadays, aluminum is less suitable: wire, film, or foil are used as materials for strain gauges [21]. These aluminums are being replaced by more flexible and practical materials, but there are aluminum alloys that have a linear stress–strain diagram, and these are used for the elastic element in some load cells. Commercial metal strain gauges have a limited sensitivity, cover very small areas, and their typical operating voltage range is less than 3% [22]. When designing strain gauges, it is necessary to achieve a high sensitivity, linearity, low hysteresis, and the temperature stability of measurements over the maximum possible range of strain variation [23]. Strain gauges have significant advantages, but there are some disadvantages associated with both temperature stability and special operating conditions. These data are summarized in Table 1.

One of the main problems faced by specialists in the field of mechanical load research is the need for the accurate measurement of stresses and strains under various operating conditions [24]. Strain gauges and strain gauge transducers provide an opportunity to perform such control, which makes this area relevant and promising for further research and development in mechanics [25]. The disadvantages associated with temperature sensitivity can most often be corrected.

Nanomaterials for strain gauges appear to be innovative, which have unique mechanical properties and the ability to respond to mechanical stress [26]. One of the main advantages of nanomaterials for strain gauges is their high sensitivity to mechanical stress at small dimensions. Due to this, such materials allow for the development of more accurate and efficient strain gauges capable of operating in a wide range of conditions [27].

Table 1

Advantages and disadvantages of strain gauge transducers [28,29,30].

№	Advantages	Disadvantages
1	High-accuracy measurement. Provides accurate and reliable force measurements, making them the ideal choice for applications where a high accuracy is required	Limited in use. When used in environments with high temperatures and aggressive environments, special protection measures are required
2	Wide measuring range. It is possible to measure both small and large forces, making them a versatile tool for a variety of applications	Minor change in sensor resistance. With a change of approximately 1%, this requires signal amplification
3	Ease of use. Easy to install and maintain, they can be used in both fixed and portable installations	Sensitivity to environmental conditions. Dependence of sensitivity on ambient humidity and corrosion formation
4	Durability. Strain gauges are made of durable materials, giving them a long service life	Accuracy. Decrease in measurement accuracy under vibration conditions

An important advantage of using nanomaterials for strain gauges is also their resistance to various external factors such as humidity, temperature, and corrosion. This increases the lifetime and performance of strain gauges, which is especially important when they are used in extreme environments or in medical devices [31,32]. Polymer-based strain gauges containing nanomaterials have a high mechanical strength, elasticity, and electrical conductivity, making them ideal for use in a variety of devices. Among the most promising nanomaterials for strain gauges are carbon nanotubes (CNTs) [33], graphene [31], carbon fibers [34], and functionalized and modified nanomaterials [26,27,28,29,30,31,32,33,34,35].

Therefore, the aim of this review study is to determine the prospects of using various nanomaterials as additives in polymers to create strain gauges. In order to achieve this objective, the following tasks were set:

• -. To consider the theoretical basis of strain gauging;

• -. To study the types of strain gauge transducers and their characteristics;

• -. To consider the possibility of using nanomaterials as filler in polymers for strain gauges;

• -. To carry out a classification of modern strain gauges.

2. Applications of Strain Gauges

The application areas of strain gauges include a wide range of devices for various purposes, which requires the use of various types of strain gauges (Figure 3) to measure physical effects [36].

Strain gauges are used in several types of measuring instruments, such as laboratory scales, industrial scales, platform scales, and universal testing machines [37,38]. The principle of the operation of strain gauges is based on the measurement of changes in the electrical resistance of a material under mechanical strain. Strain gauges also find application in the production of scales, the use of which is common in various industries [39]. The principle of the operation of electronic scales is to measure the force of gravity acting on the strain gauge and convert this force into a corresponding electrical output signal through strain.

Since 1993, the British Antarctic Survey has been installing strain gauges in fiberglass nests to weigh albatross chicks [40]. Strain gauges are used in a wide variety of products, such as the seven-post shaker that is often used to tune race cars [41]. Strain gauges are also installed in hot beverage dispensers such as those for coffee and tea (Figure 4) to dispense the right volume of liquid [42].

The column load cell is a column-type sensor used in trucks, wagons, hoppers, and capacitance scales. Other names for the sensor are cylindrical sensor, compression sensor, and “barrel” and tower load cell [43]. This load cell is made in two versions—digital or analog. Figure 5 shows a column load cell ZSFY-A/-SS (KELI sensing Technology, Wenzhou, China) mounted for measuring the mass of trucks.

Other popular applications of strain gauges are summarized in Table 2.

Thus, the main use of strain gauges can be divided into the following two categories [56,57]:

Category I—studies of physical properties of machines, structures, installations, etc., where a large number of measurement points, wide ranges of parameter changes, and the impossibility of calibrating measurement channels are required. The error in such cases ranges from 2% to 10%.

Category II—the measurement of mechanical quantities, where the sensors are graded by the measured quantity and the errors are in the range from 0.5% to 0.05%.

Figure 6 presents a block diagram of an algorithm for strain gauge selection for various technical applications (medicine, construction, science, engineering, aviation, and automotive, etc.), which includes the following components: material selection; installation; resistance measurement; the transformation of strain value; and the interpretation of the results of resistance change measurement.

The causes of measurement errors (stochastic and systematic) when using strain gauges can be related both to the measurement method, the way of its realization, and a number of external factors. The incorrect installation or fixation of the strain gauges on the object of measurement can distort the results by forming a measurement error. Excessive mechanical load on the load cell can lead to its damage or deformation. The insufficient stabilization of environmental parameters before measurement, such as temperature or vibration changes, can also affect the accuracy of the results. Improper calibration prior to measurement can lead to inaccurate results. Wear or damage to load cell components can cause distortion in the measurement data. Electrical interference can also cause measurement errors. Incorrect data processing and interpretation, as well as an insufficient understanding of the principles of strain gauge operation, can also cause errors [18].

Various methods are used to compensate for temperature error in strain gauges. One way is to use compensating elements such as thermistors or thermocouples to monitor temperature changes and adjust the measurements accordingly. Another way is to use special materials to make strain gauges that have more stable characteristics with temperature changes. Software compensation methods are also used when special algorithms are used to process the received data and correct them according to known temperature dependencies. In addition, compensation is made possible by installing temperature sensors near the strain gauges and using these data to correct the measurements.

3. Types, Kinds, and Properties of Strain Gauges

3.1. Types of Strain Gauges

To date, strain gauges can be categorized into the following three main types: wire, foil, and film (Figure 7).

As an example, Figure 7c shows a film strain gauge RFP602 (Honeywell, Morris Township, NJ, USA) for measurements in the range of 0–1 kg. RFP602 strain gauges are installed in Wavgat (Shenzhen, China) strain gauges and table electronic scales for measuring small items, e.g., precious metals. The film analog strain gauge RFP602 with a maximum allowable load of 1 kg changes resistance under the action of applied force. The diameter of the sensing part is 10 mm.

3.1.1. Wire Strain Gauges

Wire strain gauges in measurement technology are used in two main directions [58,59]. In the first case, the tenso-effect of a pressurized conductor is used. A coil of wire, usually made of manganin, is placed in the area of gas or liquid pressure measurement, and the change in the active resistance of the wire serves as the output signal of the transducer. In the second case, the tenso-effect of a tensile wire made of a stress-sensitive material is used. Strain gauges can be “free”, where the wire is fixed between two elements and acts as an elastic element or adhesive. Adhesive strain gauges consist of a wire sensor attached to a substrate using thin paper or film. The wire is usually zigzag-shaped and has a diameter from 0.02 to 0.05 mm. The ends of the wire are connected to lead wires and the sensor is coated with a layer of varnish, sometimes additionally protected with paper or felt.

3.1.2. Foil Strain Gauges

Foil strain gauges (Figure 3) are one of the most common types of adhesive sensors. Because of the possibility of increasing the area of the leads, a more reliable contact connection is provided compared to wired sensors [60,61,62]. They are a thin strip of foil from which some of the metal is removed, forming a grid with leads. The advantage of foil strain gauges is the possibility of creating a variety of meshes, which makes them more flexible. They can be used to measure both linear stresses and torques, for example, when glued to a shaft or diaphragm [63].

Compared to wire transducers, foil strain gauges offer several advantages, such as a larger surface area and smaller cross-section, which ensures their stable operation at high temperatures and with long-term loads [64]. Meanwhile, this large surface area also improves the temperature contact with the sample, which reduces self-heating. Foil voltage sensors have a high ratio of sensing element to cross-section (sensitivity). This ensures their stability at high temperatures and with long-term loads [65]. In the process of creating foil sensors, metals such as constantan and nichrome, as well as various materials, including titanium–aluminum alloy, are used. The latter provides the ability to measure strains up to 12%.

Historically, constantan wire and paper support were used. Constantan alloy is still widely used by large companies, but for foil strain gauges. Wire strain gauges are very rare today. Today, more promising and practical materials produced by such large companies, such as Vishay, HBK, Kyowa, Omega, etc., are used as materials for strain gauges. In addition, semiconductor materials are also used. Materials for foil strain gauges are presented in Table 3.

Polyimide is a common support material, while Bakelite is less commonly used for support. For constantan foil with epoxy backing, the recommended range is from about −75 to + 205 °C and the maximum temperature is from −200 to + 315 °C.

3.1.3. Strain Gauge Transducers

The third type of strain gauge transducers are film transducers. Strain gauge transducers can be made on the basis of metal or semiconductor film [66,67,68]. Figure 8 shows a semiconductor strain gauge.

The production of film strain gauges is carried out by the deposition of sensitive material on a substrate. The thin layer of such strain gauges is ~15–30 μm and has a significant advantage when measuring strains in the dynamic mode, as well as at high temperatures. Film strain gauges based on bismuth, titanium, silicon, germanium, etc., have been used [69,70,71].

They are in the form of a single conductive strip and are not subject to a decrease in sensitivity with respect to the material from which they are made. For strain gauge transducers based on metal film, the strain ratio ranges from two to four and the resistance is in the range from 100 to 1000 ohms. Transducers based on semiconductor film have a much larger range of coefficients from 50 to 200. They are more sensitive to voltage, so they do not require amplifiers. The output voltage of a semiconductor strain gauge bridge can be as high as one volt. However, note that the resistance of the semiconductor transducer varies with voltage and has a non-linear characteristic. An amplifier is required to work with a metal-film-based strain gauge. The linearity of this transducer is very high, which effectively compensates for the effect of temperature. Thus, transducers based on metal and semiconductor film have their own features, but provide the necessary functionality according to the specific requirements and application conditions [72]. This type of strain gauge transducer has a high thermal stability. An evaluation of the feasibility of a high-temperature Pt-based thin-film resistor at a temperature of 700 °C and five cycles is presented in Figure 9 [69].

Figure 9 shows an example of the possibility of thin-film strain gauge operation at high temperatures. This indicator is much higher than that of other strain gauges. However, it should be noted that extremely high and low temperatures, as a result of long-term exposure, irreversibly change the structure of thin films, due to which, they lose measurement accuracy [73]. At the same time, the technology for producing thin films is more expensive than the technology for producing foil strain gauges. In this regard, polymer nanocomposites are promising materials as strain gauges [74]. Considering the significant advantages of polymer nanocomposites, such as a wide measurement range, high flexibility and elasticity, and simple manufacturing technology, it should be noted that the polymer base is limited in temperature range [75].

3.2. Calculation of Main Parameters of Strain Gauges

The main characteristic of a strain gauge is the relative strain sensitivity coefficient K the ratio of the change in resistance to the change in conductor length, as follows:

(2)$K={\displaystyle \frac{{\epsilon }_R}{{\epsilon }_l}}$

where ${\epsilon }_R={\displaystyle \frac{\Delta R}{R}}$—is the relative change in the resistance of the conductor;

${\epsilon }_l={\displaystyle \frac{\Delta l}{l}}$—is the relative change in the conductor length.

The strain gauge coefficient K can be represented in a more popular and accurate form for calculations, which follows from Equation (1), as follows:

(3)${\epsilon }_{l}K={\displaystyle \frac{R}{R_0}}$

A change in the length of solids is associated with a change in volume, and their properties and the value of resistivity ρ change accordingly (1). The value of the strain-sensitivity coefficient is expressed from the following formula:

(4)$K=\left(1+2\mu \right)+m$

(5)$m=\left({\displaystyle \frac{\Delta \rho }{\rho }}\right)/\left({\displaystyle \frac{\Delta l}{l}}\right)$

(1 + 2μ) characterizes the change in resistance by geometric measurements (length and cross-section) of the conductor, and m characterizes the change in the specific resistance of the material by physical properties.

The manufacturing of strain gauge transducers using semiconductor materials makes it possible to determine sensitivity mainly through changes in the material properties of the grating when it is deformed. The sensitivity factor K ≈ m can vary for different materials from 40 to 200. The typical values of strain sensitivity coefficients for different materials, including carbon nanomaterials such as carbon nanotubes (CNTs) and multilayer nanotubes (MWCNTs), are summarized in Table 4.

Thus, having analyzed the main types of sensors (wire, foil, and film) and their properties, we can highlight their strengths and weaknesses, which are summarized in a comparative Table 5 [98].

3.3. Connection Method of Strain Gauge Transducers

Resistive electrical strain gauges are connected in the Wheatstone bridge as follows: quarter bridge, half bridge, and full bridge. There are several types of strain gauge transducers, according to the method of connection for measuring resistance under strain [1,15,19], as follows:

1. Half bridge. This is the most common type (Figure 9). They have two strain resistors connected as a half bridge. One resistor is in the deformed zone and the other in the non-deformed zone, which allows for compensating for temperature effects and improving measurement accuracy.

2. Full bridge. This uses four strain gauges, forming a full-bridge circuit. This provides a high sensitivity and stability in strain measurement.

3. Multi-point strain gauges. These transducers have multiple sensing elements to measure strains at different points on the object. This is useful for estimating stress distributions.

4. Integral. These are also referred to as “voltage sensors”. They are built directly into the design and can measure voltages in real time.

5. Centrally symmetrical. They are used for measuring uniaxial deformations. They have two sensing elements arranged symmetrically about the center.

Each type of strain gauge transducer has a number of features that allow for its application depending on the required accuracy, type of deformation, and other measurement parameters. Figure 10 shows a half-bridge strain gauge transducer.

Many load cells use strain gauges in a full bridge. The Wheatstone bridge compensates for temperature effects and eliminates signals caused by external forces [1]. Temperature, the length of wire used to close the circuit, and the placement of strain gauges will affect the resistance in the Wheatstone bridge, resulting in errors in the measured value. In precision load cells, these effects can be compensated for by adding resistance to the bridge [15].

Multi-point strain gauges (chains of strain gauges) are used in areas of stress concentrators, where there are gradients of stress and strain. Usually there can be 5–10 strain gauges on the same support (Figure 3c), but each strain gauge is connected to the Wheatstone bridge in a quarter bridge or half bridge.

There are various resistive strain gauges available for different applications, some of which are described above. Each strain gauge is designed to measure strain along a well-defined axis so that it can be properly aligned with the strain field [1,19].

3.4. Classification of Load Cells

The nominal value of the maximum perceived load ranges from 5 N to over 50 MN. This has become the most widely used of all measuring systems and can be used as a standard for force transmission with high-resolution digital displays [1]. At the same time, load cells differ depending on the type of load and their design features. Cantilever (beam), S-beam, diaphragm (washer), column (rod), and torsion load cells are used for different types of measurements (Figure 11).

To summarize the information presented, strain gauges can be classified based on several factors, as shown in Figure 12.

Usually, strain gauges are connected in a full bridge, not a half bridge (Figure 10).

4. Strain Gauges Based on Polymer Composites Containing Carbon Nanostructures

Recently, there has been considerable interest in the development of strain gauges based on polymers with conductive fillers [99]. One option for producing strain gauges is to use polymers filled with conductive materials and, in particular, carbon-dispersed structures [100]. Among carbon nanomaterials (Figure 13), the most effective are CNTs [101], the use of which allows for measuring small deformations with a high accuracy [102,103]. At the same time, CNTs have a high strength and elasticity, which allows for creating very sensitive sensors. Graphene is an allotropic modification of carbon, which has a high electrical conductivity and can be used to create sensors with a fast response and high measurement accuracy.

MWCNTs show good results in the field of strain gauge creation, which is related to their unique electromechanical properties [85,86,87,88,89,90,91,92,93,94,95,96,97,103,104,105]. Studies conducted in the field of strain gauges show which aspects of using CNTs for strain measurement, both at the nano and macro levels, are of great importance. In this case, the main method for obtaining a polymer composite containing CNTs is mixing, as shown in Figure 14.

First of all, CNTs undergo changes in their band structure under the influence of mechanical deformations [106]. The electrical resistance of CNTs increases linearly with an increasing strain, which makes them an ideal material for piezoresistive strain sensors. Conductive composite films can be made by blending single-walled or multi-walled CNTs with polymers to improve the performance of strain sensors [107]. Studies also show that CNTs exhibit a stable and predictable stress response as a function of temperature.

It should be noted that polymer nanocomposites have a high calibration coefficient and stable response to mechanical stress [108]. Nanocomposites based on polymer matrices are optimal for measuring large deformations (>10%), which is especially important for applications such as intelligent robots and human motion monitoring. When a densely packed array of CNTs is stretched, the configuration of their network changes, which leads to a change in its electrical resistance (ΔR) [109], as shown in Figure 15.

The polymer coating the CNT array affects its piezoresistive response not only during the first loading, but also during subsequent (cyclic) loading [110]. Such a response may depend on the dielectric and mechanical properties of the polymer coating (Figure 16).

This is mainly influenced by the contact between individual CNTs, tunneling, and electron hopping, which depend on the distance between individual CNTs (Figure 17).

5. Dispersed Fillers of Polymer Composites for Strain Gauges (Electrical Conductivity Mechanisms)

Almost all existing natural or synthetic materials can serve as polymer fillers after giving them a given shape, size, and structure; these are often carbon nanomaterials [111].

There are three main mechanisms of electric charge transport in a polymer composite containing dispersed conductive fillers [112,113], as follows:

1. Electrical percolation;

2. Tunnel effect;

3. Quantum hopping.

Theoretically, the percolation mechanism of electrical conductivity can be represented in the first approximation as a power law reflecting the dependence of the conductivity of the material on the concentration of the conducting component, i.e., the electrophysical transition of the composite from a conducting state to an insulating one (dielectric) [114], as follows:

(6)$\sigma ={\sigma }_0{\left(\phi -{\phi }_c\right)}^t$

where σ₀—constant;

φ—volume concentration of the conducting phase with conductivity;

φ_c—percolation threshold or critical concentration (percolation threshold);

t—critical index (exponent) of electrical conductivity, which is usually associated with the dimensionality of the conductive filler.

For 3D materials, including those with pores, the theoretical value, i.e., the parameter t, determines the power dependence of conductivity on the CNT content, and is observed in many two-phase materials (metal-dielectric). Significant deviations from this value can be explained by a decrease in the particle size of the conductive filler, as well as the contact area between the conductive elements and its nature (in particular, if tunnel contacts are realized between the conductive particles instead of conventional ohmic ones [115]).

The range of changes in φ_c is associated with the diversity of composite structures, for example, different variations of CNT/polymer, and is largely determined by the technological mode of obtaining the filler, as follows: particle size, dispersion character, method of processing electrically conductive particles (Figure 18), etc. Thus, the percolation threshold should be determined experimentally by the content of the electrically conductive phase, and not theoretically (Figure 19).

The percolation threshold depends on the shape of the filler particles; if the particles are elongated or the particles have a scaly profile, then the value of φ_c is less than that of particles with a smaller length and diameter, as well as spherical particles and a greater porosity, due to the smaller contact area between the particles.

Particles with the same length-to-diameter ratio, but introduced into different polymers, have different φc values. It should also be taken into account that the type of conductivity of CNTs strongly depends on their chirality, that is, on the symmetry group to which a specific nanotube belongs, and it obeys the simple following rule: if the indices of a nanotube are equal to each other or their difference is divisible by three, then the nanotube is a semi-metal; in any other case, they exhibit semiconductor properties. Structural defects in CNTs manifest themselves in a significant increase in resistance. As a result of CNT synthesis, some nanotubes have semiconductor properties, and others have metallic properties, with the electrical conductivity of individual tubes being in the range of 1.7–1.8 S/cm.

At the same time, the percolation theory does not describe two- and three-component mixed fillers for more complex composite materials. The tunnel effect and quantum hopping occur in the case of the polarization of the polymer composite as a result of the action of an electromagnetic field. In some cases, the tunnel effect is more pronounced, and in others, quantum hopping is. This is primarily due to the influence of temperatures. At high temperatures, the polymer composite exhibits quantum hopping rather than tunneling. This may be due to the thermoresistive effect in the CNTs themselves [112]. As a result, some changes in the geometric dimensions of the CNTs occur.

The polymer matrix and methods for its modification with various dispersed fillers greatly affect the properties of strain gauges [113,116]. Metal fillers for strain gauges are known [117,118,119]. However, their cost is higher than that of CNTs. At the same time, CNTs are smaller in mass and have a better bulk density, which is necessary for filling the polymer matrix. Table 6 presents the parameters of strain gauges based on polymer composites.

6. Effect of Temperature Coefficient of Resistance (TCR) on Strain Sensitivity of Polymer Nanocomposites

Thin-film CNT sensors also exhibit resistance hysteresis under cyclic strain loading [130], which is due to the irreversible degradation of the CNT/polymer interface. Temperature can also cause changes in the electrical resistance of the strain gauge. For piezoresistive strain gauges, these temperature-induced changes in electrical resistance can be misinterpreted as strain. Thus, the thermoresistive response of strain gauges also needs to be characterized to account for potential temperature compensation factors of the strain gauges.

Commercial strain gauges have a sensitivity factor of two with a compensated temperature coefficient of resistance (TCR). In this case, it is necessary to use strain gauge materials with a high calibration factor and a small TCR. The effect of the self-compensation of strain gauges can be achieved by combining a semiconductor material with a negative TCR with a high calibration factor and a metal with a positive TCR, leading to a TCR close to zero. Alternatively, nickel-containing diamond-like carbon films (Ni-DLC or aC:H:Ni) and Ag-ITO compounds can be used, which allows for achieving zero-crossings in the TCR and calibration factors above 10 [76].

The geometry of the conductive mesh of a CNT strain gauge has an important effect on its piezoresistive response [131]. The main physical mechanism of sensitivity to mechanical action is based on a change in geometric dimensions that occurs during deformation from an external effect, which leads to a change in the electrical resistance of the sensor material, which is measured using controllers with analog-to-digital converters [132]. The following three calibration methods can be used to improve the accuracy of sensors: single-point, two-point, and three-signal [133]. The optimal option is a direct connection of the strain gauge to the microcontroller [134], and in this regard, strain gauges should provide good metrological characteristics and accurate measurements of small and large deformations. The use of a polymer matrix type is of key importance in the formation of a strain gauge [135]. The cohesion of filler particles and their dispersion in the composite depend on it, affecting the mechanical and electrophysical characteristics of strain gauges based on them [136]. Improving the distribution of MWCNTs in the polyurethane (PU) matrix reduces the percolation threshold and improves the electrical conductivity and strain-sensing properties of MWCNT-filled PU nanocomposites. In this way, the calibration coefficients can be improved in both small and large strain regimes. Elastomers with a uniform distribution of CNTs have an increased strain resistance, as well as improved strength and tunable sensitivity. In [137], it was shown that the resistance of CNT/polymer strain gauges changes with time, both with and without strain, which leads to several limitations that need to be overcome before CNTs can be used as sensing materials for polymer composite strain gauges. It is necessary to improve the reproducibility of the measurement results, as well as their stability. Reproducibility is related to the repeatability of the resistance–strain characteristics with the stability of the measured resistance over a long period of strain gauge operation. The resistance of CNT thin films varies depending on a number of factors, such as strain, defects, temperature, chemical influences, and size effects [138].

Thus, polymers filled with CNTs are promising materials possessing a number of properties preferable for strain measurement, such as flexibility, resistance to aggressive environments (anti-corrosion properties), small weight and size dimensions, etc. At the same time, in polymer composites, the strain sensitivity characteristics can be tuned for various applications by changing the morphology of the conductive structures and composition. The conductivity of such composites usually changes non-linearly and has an exponential character, while the conductivity of the matrix increases significantly (by several orders of magnitude) upon reaching the percolation threshold. With an increasing deformation or under compressive stress, the geometry and length of the conductive networks present in the matrix change, which, in turn, leads to a deformation-dependent change in electrical resistance [108,139]. In most cases, such changes are reversible and have a wider range than the changes observed in their metallic analogs. The diversity of characteristics and the wide range of electrophysical properties observed in polymers modified with carbon nanomaterials allow them to be classified in the so-called class of “intelligent” or “smart” materials for strain gauge measuring transducers (strain sensors) [85,86,87,88,89,90,91,92,93,94,95,96,97,140].

It is necessary to take into account modern technological capabilities when using polymer composites associated with the use of 3D printers [141], which allows for obtaining sensors with stable parameters [142]. Therefore, despite the obvious advantages of strain gauges based on polymers modified with dispersed conductive structures, there are problems in creating effective strain gauges with the ability to operate under conditions of large deformations with an improved sensitivity and measurement accuracy, that is, directly implementing the effect of the self-compensation of strain gauges when combining a semiconductor material with a negative TCR with a high calibration coefficient and a metal with a positive TCR, as well as improved resource characteristics, allowing for long-term operation with multiple compression/decompression modes. At the same time, individual tasks associated with strain measurement require their own approach, which can be implemented based on the selection of various options for polymer matrices and synthesized conductive metallized carbon nanostructures [143].

7. Modern Strain Gauge Technologies Using Polymer Composites

There are several emerging trends and developments in strain measurement that are making significant contributions to modern strain and stress measurement techniques [139,144,145,146], as follows:

1. Nanotechnology. The use of nanomaterials in strain measurement allows for the creation of more sensitive and compact sensors. Nanotechnology allows for the creation of strain gauges with improved mechanical and electrical properties. Nanomaterials have unique properties that make them ideal for use in strain gauges. The use of nanotechnology in strain measurement also allows for the creation of wireless sensors that use nanomaterials to transmit data wirelessly. This opens up new possibilities for monitoring and controlling various processes, as sensors can be placed in hard-to-reach places without the need for wired communication [147].

2. Wireless strain gauges. The development of wireless communication technologies allows for the creation of strain gauges that can transmit strain and stress data wirelessly. This is especially useful in cases where wired connections are inconvenient or impossible. Wireless strain gauges are strain gauge transducers that can transmit data without using wires. They are widely used in various fields where it is necessary to measure stress, strain, or weight and transmit these data to a remote device for analysis or monitoring. This is especially convenient in cases where wires may be damaged or interfere with the environment. Wireless strain gauges can be used in various fields such as medicine, the automotive sector, construction, industry, and sports. They provide the accurate and reliable measurement and transmission of data, which makes them an important element in modern technologies [146]. However wireless technology is also used for metallic strain gauges.

3. Integration with the Internet of Things (IoT). Strain gauges integrated with IoT technologies can transmit strain and strain data in real time, which allows for monitoring and controlling the condition of structures and equipment remotely. Integrating strain gauges with IoT opens up new prospects for monitoring and controlling various processes. Connecting strain gauges to the IoT network allows for transmitting strain and stress data in real time to a remote server for analysis and decision making [148]. Data on deformations and stresses can be transmitted in real time, which allows for a prompt response to changes and the necessary adjustments. Thanks to the internet connection, data from strain gauges can be accessed from anywhere in the world, which is especially important for the remote monitoring of objects. The use of IoT allows for the automation of data collection and analysis processes, which reduces the risk of errors and increases the efficiency of the monitoring system. Accurate and timely information on deformations and stresses makes it possible to use resources more efficiently and prevent emergency situations [149].

4. Data modeling and analysis. Modern methods of machine learning, data analysis, and artificial intelligence (AI) allow for the more accurate and efficient processing of data obtained from strain gauges, identifying patterns and predicting the behavior of structures and materials [150,151].

5. Miniaturization and integration. New developments are aimed at creating more compact and lightweight strain gauges, which makes them more convenient to use and allows for an expansion of their scope of application. These new trends and developments in strain gauge technology promise to significantly improve the accuracy, ease of use, and wide range of applications of strain gauges in various industries and sciences [152,153].

The development of strain gauge technology promises to be innovative and exciting. New materials and technologies will enable the creation of more sensitive and resolving strain gauges. Integration with other sensors and technologies, such as microcontrollers and optical systems, will increase their functionality. Wireless data transmission technologies will make their installation and use more convenient. Software developments will improve data analysis and processing. New calibration and error compensation methods will increase measurement accuracy. All of this will make strain gauges more accurate, convenient, and versatile for various fields of science and industry.

In addition, trends in strain gauge development point to wider application in various fields such as biomedicine, sports, robotics, and the automotive industry. The development of hybrid and integrated systems will allow for the creation of more compact and efficient devices for measuring stress and strain. Improvements in the environmental and energy characteristics of strain gauges are also expected, which will facilitate their wider application in various areas of life, including miniature devices.

In addition, nanomaterials and nanotechnologies aimed at creating polymer composite materials will be able to create strain gauges with an even higher sensitivity and resolution. The use of artificial intelligence and machine learning in the analysis of strain gauge data will improve the accuracy and speed of information processing. There is also a tendency to create more flexible and universal strain gauges capable of operating in various conditions and on various surfaces, which will make them more attractive for a wide range of applications. It should be noted that the further development of nanotechnology and synthesis methods will make it possible to create even more advanced nanomaterials for strain gauges with improved characteristics and new functionality. This opens up broad prospects for the use of such materials in various fields. There are four main areas of application of polymer composite strain gauges, as follows:

1. Medicine. Nanomaterials make it possible to create thin and flexible strain gauges based on biologically safe polymers, which can be used to monitor biomechanical parameters in medical applications, such as measuring vascular pressure or monitoring cardiac function [51,52,53,154,155].

2. Construction and engineering. Nanomaterials make it possible to create strain gauges with a high accuracy and sensitivity for monitoring stresses and strains in structures and machines [44,45,46,156,157,158,159,160].

3. Electronics. Nanomaterials can be used to create ultra-thin strain gauges that can be integrated into electronic devices for measuring mechanical parameters [135,161].

4. Technological processes in the chemical industry. These can measure the level of cavitation in liquids with various parameters, including aggressive environments [162].

In general, the prospects for the development of strain gauge technology promise a significant improvement in its characteristics and an expansion of its scope of application.

8. Prospects for Using Polymer Composites with Nanomaterials for Strain Gauges

Flexible electronics are devices that consist of electronic materials and/or circuits integrated into a flexible substrate. Compared to rigid printed circuit boards, flexible electronic circuits have the ability to mechanically bend, twist, compress, and stretch due to the use of soft polymeric materials (substrates) [11,163].

Flexible electronic devices have attracted increasing attention from researchers worldwide because they have the potential for application in many innovative fields such as microelectronics, biomedical engineering, healthcare monitoring (sensors), robotics, electronic shells, and human–machine interfaces [164,165,166]. Given the dynamics of the synthesis of new nanomaterials and nano-industry technologies over the past decades, the development of polymer composites with nanomaterials for strain gauges will enable the creation of new-generation devices that can complement traditional strain gauges in a broad sense [167,168,169].

The progressive development of innovative technologies in the field of stretchable conductors has paved the way for the development of body-attached portable electronic devices. Strain sensors developed using stretchable conductors allow for the monitoring of physical, chemical, and environmental conditions with minimal discomfort [154,170,171,172,173]. The typical mechanisms that strain sensors use are changes in resistance or changes in capacitance in response to deformation [174].

9. Conclusions

Thus, in accordance with the objectives of the review study, the following conclusions can be drawn:

1. Strain measurement plays a key role in modern measurement technologies, providing accuracy and reliability in measuring strains and stresses in various materials and structures;

2. The progressive development of innovative technologies in the field of stretchable conductors has paved the way for the development of body-attached portable electronic devices. Strain sensors developed using stretchable conductors allow for the monitoring of physical, chemical, and environmental conditions;

3. With the advent of new technologies in the field of nanomaterials and microelectronics, the further development of strain measurement is expected, including the creation of more accurate and compact transducers with improved characteristics.

4. The use of strain measurement is not limited to the field of strength of materials, but also finds application in medicine, the automotive sector, aerospace, and other areas where accurate measurements of strains and stresses are required.

5. Further research in the field of strain measurement will create more efficient and innovative measurement methods, contributing to the development of science and technology in general. The development of nanoelectronics and nanomaterials technologies opens up new opportunities for creating more sensitive and compact strain gauge transducers. Nanomaterials such as carbon nanotubes or graphene can be used to create highly sensitive sensors with a low power consumption.

6. An important area of strain gauge development is improving methods for compensating for temperature effects on measuring devices. This will improve the accuracy of measurements (reduce the error) in a wide range of temperatures and operating conditions.

7. With the development of the Internet of Things (IoT) and smart technologies, strain gauges can become a key technology for monitoring the conditions of infrastructure, building structures, vehicles, and other objects, which will make them even more in demand in various industries. An important aspect of strain gauge development is also improving the methods for processing and analyzing data obtained from strain gauge transducers. This will help to improve the accuracy and reliability of the measurement results.

8. Despite the obvious advantages of strain gauges based on polymers modified with dispersed conductive structures, there are problems in creating effective strain gauges that have the ability to operate under conditions of large deformations with an improved sensitivity and measurement accuracy.

Author Contributions

Conceptualization, A.V.S. (Aleksei V. Shchegolkov) and A.V.S. (Alexander V. Shchegolkov); software, M.A.C.; validation, V.V.K. and M.A.C.; formal analysis, M.A.C.; investigation, A.V.S. (Aleksei V. Shchegolkov); resources, A.V.S. (Alexander V. Shchegolkov); data curation, M.A.C.; writing—original draft preparation, A.V.S. (Aleksei V. Shchegolkov); writing—review and editing, A.V.S. (Aleksei V. Shchegolkov); visualization, A.V.S. (Aleksei V. Shchegolkov); supervision, V.V.K.; project administration, A.V.S. (Alexander V. Shchegolkov); funding acquisition, A.V.S. (Aleksei V. Shchegolkov) All authors have read and agreed to the published version of the manuscript.

Data Availability Statement

The data presented in this study are available on request from the first author.

Acknowledgments

This work was carried out with the financial support of the Ministry of Science and Higher Education of the Russian Federation (State assignment FZRR-2024-0003).

Conflicts of Interest

The authors declare no conflicts of interest. The funders had no role in the design of the study; in the collection, analysis, or interpretation of the data; in the writing of the manuscript; or in the decision to publish the results.

Abbreviations

TCR	temperature coefficient of resistance;
NTR	negative temperature coefficient of resistance;
PTR	positive temperature coefficient of resistance;
CNT	carbon nanotubes;
MWCNTs	multiwalled carbon nanotubes;
PDMS	polydimethylsiloxane;
PU	polyurethane;
PMVS	Polyvinyl Methyl Siloxane;
TPU	thermoplastic polyurethane;
IoT	Internet of Things;
AI	artificial intelligence

Footnotes

Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Figures and Tables

Figure 1. Strain gauge design: (a)—in longitudinal section: 1—coating; 2—grid; 3—substrate; and 4—external lead; (b)—top view; and (c)—wire in section (0.001-inch diameter).

Figure 2. Linear strain gauge: (a)—working principle of foil strain gauge: 1—wire grid; 2—support; 3—contacts; and L—base and (b)—wire-on-paper strain gauge (sample of the 60 s).

Figure 3. Different applications of foil gauge strain gauges: (a) and (b)—single and (c)—multi-point.

Figure 4. Hot beverage filling machine.

Figure 5. Installation and mounting of column load cell ZSFY-A/-SS: 1—foundation; 2—lower baseplate; 3—duster; 4—upper cup; 5—upper baseplate; 6—loading platform; 7—M8 screw; 8—load cell; 9—lower cup; and 10—eccentric.

Figure 6. Algorithm for selecting strain gauges for different applications.

Figure 7. Types of strain gauge: (a)—foil; (b)—wire; and (c)—film (commercial device).

Figure 8. Semiconductor strain gauge.

Figure 9. Strain output of a high-temperature Pt thin-film thermistor at 700 °C, 5 cycles [69].

Figure 10. Full-bridge circuit (simplified circuit).

Figure 11. Load cells by the shape of the load-bearing base: (a)—cantilever; (b)—cylindrical; and (c)—S-shaped.

Figure 12. Classification of strain gauges.

Figure 13. Carbon nanostructures in different dimensions.

Figure 14. Schematics of the MWCNT/PVA-based humidity sensor production process.

Figure 15. Schematic for the alignment of CNTs in the composites by uniaxial stretching and network rearrangement.

Figure 16. (a) Schematical illustration of a strain sensor based on CPHs and (b) the piezoresistivity mechanism of a PVA-PPy strain sensor when applying small strain.

Figure 17. Percolation process in conductive composites.

Figure 18. Structure of the conductive polymer nanocomposite before and after treatment: (a)—before treatment of CNTs in the polymer, pronounced agglomeration of CNT particles; and (b)—treated CNTs in the polymer, conductive phase.

Figure 19. Schematic diagram of the dependence of logarithmic conductivity on the concentration of CNTs (vol. %), illustrating the S-shaped percolation curve.

Table 2

Application areas of strain gauges.

Application Area	Measurement	Purpose	Ref.
Mechanical engineering	Control of structural strength	Determination of stresses in machine parts and mechanisms to prevent destruction	[29,44,45,46,47]
	Vibration monitoring	Analysis of vibration loads on structural elements
	Study of fatigue characteristics of materials	Determination of the service life of parts under cyclic loads
	Quality control of welded seams	Evaluation of the strength of welded joints
Construction	Stress control in structures	Determination of stresses in reinforced concrete structures, bridges, and buildings	[44,45,46]
	Monitoring of foundation deformations	Control of settlement of buildings and structures
	Study of the behavior of materials under various loads	Determination of deformation characteristics of building materials
Aviation and space industry	Strength testing of aircraft, including drones	Determination of stresses in structural elements of aircraft and rockets	[47,48]
	Study of the behavior of materials under extreme conditions	Study of the behavior of materials at high temperatures, pressures, and vibrations
Automotive industry	Body and suspension strength control	Determination of stresses in elements of the car body and suspension	[49,50]
	Development of new materials	Research on new materials for the automotive industry
Medicine	Measurement of biomechanical parameters	Study of joint movement and muscle strength	[51,52,53]
	Creation of prostheses and orthoses	Load control on prostheses and orthoses
Geology and geophysics	Measuring stresses in rocks	Determination of the state of rock masses for the prediction of rockfalls and landslides	[7,54,55]
	Monitoring seismic activity	Study of deformations of the Earth’s crust

Table 3

Materials for foil strain gauges.

№	Materials
	Load Cell	Support
1	Constantanium foil,	Polyimide; Bakelite
2	Nichrome foil, nichrome wire	Removable Teflon glass strip
3	Isoelastic wire	Bakelite,
4	Dynaloy foil	Polyimide
5	Stabiloy foil, Stabiloy wire	Polyimide
6	Platinum-tungsten wire	Removable Teflon glass strip

Table 4

Materials for strain gauge.

№	Sensitive Material	K	Substrate	Ref.
1	Me = W, Ti и Ni (film)	>10	DLC	[76]
2	Ag-ITO	4–7	DLC	[76]
3	TiAlNxO	2.2–2.5	Sapphire	[77]
4	AlN/Pt	≤4.7	Al2O3	[78]
5	Pt/SiO2	18	Si-wafers	[79]
6	Invar36	2.5–4.5	Microslides	[80]
7	NiCr	2.5	Ni-base superalloy	[73]
8	Pt	1.7–1.9	Ni-base superalloy	[69]
9	Pt	1.9–2.5	Sapphire	[81]
10	MXene/MWCNTs	646	PDMS	[4]
11	MXene	178	PDMS	[82]
12	MXene	228	polyurethane	[83]
13	CNTs	7.22	PDMS	[84]
14	MWCNTs	9	PDMS	[85]
15	MWCNTs	181.36	Graphene platelets	[86]
16	MWCNTs	4.3	PDMS	[87]
17	MWCNTs	513	PDMS	[88]
18	MWCNTs	22	TPU	[89]
19	MWCNTs	1–1.5	Silicone polymer	[90]
20	MWCNTs	34.38	Silicone rubber	[91]
21	MWCNTs	43.4	Graphite films	[92]
22	MWCNTs	2800	TPU	[93]
23	MWCNTs	12.15	PDMS	[94]
24	MWCNTs	2.4	Eraser	[95]
25	MWCNTs	4.5	PDMS	[96]
26	MWCNTs	513	PDMS	[97]

Note—PDMS—flexible polydimethylsiloxane (PDMS) substrate and TPU—thermoplastic polyurethane substrate.

Table 5

Comparative table of characteristics of strain gauges.

Characteristic	Wire	Foil	Film
Accuracy	Average	High	Average
Linearity of characteristics	Average	High	Low
Sensitivity	High	Average	Very high
Strength	High	Low	Average
Stability of characteristics	Average	High	High
Cost	Average	Average	High
Dimensions	Large	Small	Very small

Table 6

Parameters of flexible strain gauges.

№	Polymer	Conductive Fillers	Gauge Factor	Working Strain, %	Ref.
1	Fluoroelastomer	CNTs	1.36 × 105	85–100	[120]
2	TPU	MWCNT	5200	5–50	[121]
3	TPU	SWCNT/RGO	114.7	200–300	[122]
4	TPU	Graphene pellets	80	50–100	[123]
5	TPU	Graphene	5.9	95–100	[124]
6	TPU	rGO	79	10–100	[125]
7	Epoxy resin	CNTs	0.6–14	6	[126]
8	PMVS	CNTAs/CB	10	0–60	[127]
9	Nitrile elastomers	Graphite nanoflakes	868.12 ± 56.90	30	[128]
10	PU	MWCNTs	62.37	80	[129]

References

1. Kamble, V.A.; Shinde, V.D.; Kittur, J.K. Overview of Load Cells. J. Mech. Eng.; 2020; 6, pp. 22-29.

2. Yao, H.; Cao, H.; Li, J. Design and Implementation of a Portable Wireless System for Structural Health Monitoring. Meas. Control; 2016; 49, pp. 23-32. [DOI: https://dx.doi.org/10.1177/0020294015615895]

3. Choe, J.K.; Kim, J.; Song, H.; Bae, J.; Kim, J. A soft, self-sensing tensile valve for perceptive soft robots. Nat. Commun.; 2023; 14, 3942. [DOI: https://dx.doi.org/10.1038/s41467-023-39691-z] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/37402707]

4. Wang, F.; Yu, H.; Ma, X.; Lv, X.; Liu, Y.; Wang, H.; Wang, Z.; Chen, D. A Highly Sensitive Strain Sensor with Self-Assembled MXene/MultiWalled Carbon Nanotube Sliding Networks for Gesture Recognition. Micromachines; 2024; 15, 1301. [DOI: https://dx.doi.org/10.3390/mi15111301]

5. Tuli, A.; Singh, A.P. Polymer-based wearable nano-composite sensors: A review. Int. J. Polym. Anal. Charact.; 2023; 28, pp. 156-191. [DOI: https://dx.doi.org/10.1080/1023666X.2022.2161737]

6. Abubakre, O.K.; Medupin, R.O.; Akintunde, I.B.; Jimoh, O.T.; Abdulkareem, A.S.; Muriana, R.A.; James, J.A.; Ukoba, K.O.; Jen, T.-C.; Yoro, K.O. Carbon nanotube-reinforced polymer nanocomposites for sustainable biomedical applications: A review. J. Sci. Adv. Mater. Devices; 2023; 8, 100557. [DOI: https://dx.doi.org/10.1016/j.jsamd.2023.100557]

7. Ma, H.; Wang, J.; Qian, J.; Luo, Q.; Wei, X. Experimental investigations of fractured rock deformation: A direct measurement method using strain gauges. J. Struct. Geol.; 2023; 171, 104869. [DOI: https://dx.doi.org/10.1016/j.jsg.2023.104869]

8. Pástor, M.; Živcák, J.; Puškár, M.; Lengvarský, P.; Klacková, I. Application of Advanced Measuring Methods for Identification of Stresses and Deformations of Automotive Structures. Appl. Sci.; 2020; 10, 7510. [DOI: https://dx.doi.org/10.3390/app10217510]

9. Dubey, K.A.; Mondal, R.K.; Grover, V.; Bhardwaj, Y.K.; Tyagi, A.K. Development of a novel strain sensor based on fluorocarbon–elastomeric nanocomposites: Effect of network density on the electromechanical properties. Sens. Actuators A Phys.; 2015; 221, pp. 33-40. [DOI: https://dx.doi.org/10.1016/j.sna.2014.10.036]

10. Festin, N.; Plesse, C.; Pirim, P.; Chevrot, C.; Vidal, F. Electro-active Interpenetrating Polymer Networks actuators and strain sensors: Fabrication, position control and sensing properties. Sens. Actuators B Chem.; 2014; 193, pp. 82-88. [DOI: https://dx.doi.org/10.1016/j.snb.2013.11.050]

11. Cetin, M.S.; Toprakci, H.A.K. Flexible electronics from hybrid nanocomposites and their application as piezoresistive strain sensors. Compos. Part B Eng.; 2021; 224, 109199. [DOI: https://dx.doi.org/10.1016/j.compositesb.2021.109199]

12. Pratt, L.; Bisson, C.; Warin, T. Bringing advanced technology to strategic decision-making: The Decision Intelligence/Data Science (DI/DS) Integration framework. Futures; 2023; 152, 103217. [DOI: https://dx.doi.org/10.1016/j.futures.2023.103217]

13. Tung, S.; Witherspoon, S.R.; Roe, L.A.; Silano, A.; Maynard, D.P.; Ferraro, N. A MEMS-based flexible sensor and actuator system for space inflatable structures. Smart Mater. Struct.; 2001; 10, 1230. [DOI: https://dx.doi.org/10.1088/0964-1726/10/6/312]

14. Sharma, S.; Verma, A.; Rangappa, S.M.; Siengchin, S.; Ogata, S. Recent progressive developments in conductive-fillers based polymer nanocomposites (CFPNC’s) and conducting polymeric nanocomposites (CPNC’s) for multifaceted sensing applications. J. Mater. Res. Technol.; 2023; 26, pp. 5921-5974. [DOI: https://dx.doi.org/10.1016/j.jmrt.2023.08.300]

15. Tutak, P. Application of Strain Gauges in Measurements of Strain Distribution in Complex Objects. JACSM; 2014; 6, pp. 135-145. [DOI: https://dx.doi.org/10.1515/jacsm-2015-0004]

16. Keil, S. On the strain gage’s 50th jubulee—A review of its evolution and of 33 years strain gage production at Darmstadt. RAM; 1988; 4, pp. 39-48.

17. Stein, P.K. Strain gage history and the end of the twentieth century. Exp. Techn.; 2001; 25, pp. 15-16. [DOI: https://dx.doi.org/10.1111/j.1747-1567.2001.tb00011.x]

18. Hoffmann, K. An Introduction to Stress Analysis and Transducer Design Using Strain Gauges; HBM Test and Measurement 2012; 240.Available online: https://mpe.au.dk/fileadmin/www.ase.au.dk/Filer/Laboratorier_og_vaerksteder/Instrument_Depotet/Udstyr/Strain_gauges/HBM_Karl-Hoffmann_An-Introduction-to-Stress-Analysis-using-Strain-Gauges.pdf (accessed on 1 November 2024).

19. İrsel, G. Research on electrical strain gages and experimental stress analysis: Case study for a full wheatstone bridge. Dicle Üniversitesi Mühendislik Fakültesi Mühendislik Dergisi; 2021; 12, pp. 783-792. [DOI: https://dx.doi.org/10.24012/dumf.1051434]

20. Hidalgo-López, J.A. Direct interface circuits for resistive sensors affected by lead wire resistances. Measuremen; 2023; 218, 113250. [DOI: https://dx.doi.org/10.1016/j.measurement.2023.113250]

21. Schomburg, W.K.; Rummler, Z.; Shao, P.; Wulff, K.; Xie, L. The design of metal strain gauges on diaphragms. J. Micromech. Microeng.; 2004; 14, 1101. [DOI: https://dx.doi.org/10.1088/0960-1317/14/7/033]

22. Mao, N.; Enrique, P.D.; Chen, A.I.; Zhou, N.Y.; Peng, P. Dynamic response and failure mechanisms of a laser-fabricated flexible thin film strain gauge. Sens. Actuators A Phys.; 2022; 342, 113655. [DOI: https://dx.doi.org/10.1016/j.sna.2022.113655]

23. Han, J.-H.; Min, S.J.; Kim, J.H.; Min, N.K. Reciprocating Arc Silicon Strain Gauges. Sensors; 2023; 23, 1381. [DOI: https://dx.doi.org/10.3390/s23031381] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/36772420]

24. Hesse, J.; Gardner, J.W.; Göpel, W. Sensors for Automotive Technology; Wiley-VCH Verlag: Weinheim, Germany, 2003.

25. Stepanova, L.; Kabanov, S.; Matveeva, I.; Chernova, V. Strength Tests of Carbon Plastic Samples Using Dynamic Tensometry. Transp. Res. Procedia; 2021; 54, pp. 220-227. [DOI: https://dx.doi.org/10.1016/j.trpro.2021.02.067]

26. Mehmood, A.; Mubarak, N.M.; Khalid, M.; Walvekar, R.; Abdullah, E.C.; Siddiqui, M.T.H.; Baloch, H.A.; Nizamuddin, S.; Shaukat, M. Graphene based nanomaterials for strain sensor application—A review. J. Environ. Chem. Eng.; 2020; 8, 103743. [DOI: https://dx.doi.org/10.1016/j.jece.2020.103743]

27. Yee, M.J.; Mubarak, N.M.; Abdullah, E.C.; Khalid, M.; Walvekar, R.; Karri, R.R.; Nizamuddin, S.; Numan, A. Carbon nanomaterials based films for strain sensing application—A review. Nano-Struct. Nano-Objects; 2019; 18, 100312. [DOI: https://dx.doi.org/10.1016/j.nanoso.2019.100312]

28. The Technical Staff of Measurements Group, Inc. Strain Gage Based Transducers. Their Design and Constrution; Measurements Group, Inc.: Raleigh, NC, USA, 1988; 72.Available online: https://mhforce.com/wp-content/uploads/2022/10/SGBT.pdf (accessed on 1 November 2024).

29. Bartz, M.; Häußler, F.; Halmos, F.; Ankenbrand, M.; Jüttner, M.; Roudenko, J.; Wirsching, S.; Reichenberger, M.; Franke, J.; Wartzack, S. Use of Printed Sensors to Measure Strain in Rolling Bearings under Isolated Boundary Conditions. Lubricants; 2023; 11, 424. [DOI: https://dx.doi.org/10.3390/lubricants11100424]

30. Yan, W.; Fuh, H.-R.; Lv, Y.; Chen, K.Q.; Tsai, T.-Y.; Wu, Y.-R.; Shieh, T.-H.; Hung, K.-M.; Li, J.; Zhang, D. et al. Giant gauge factor of Van der Waals material based strain sensors. Nat. Commun.; 2021; 12, 2018. [DOI: https://dx.doi.org/10.1038/s41467-021-22316-8]

31. Khodke, M.; Chavan, U.; Joshi, S.; Shinde, S. Experimental studies on carbon nanotube strain sensors. Mater. Ttoday Proc.; 2023; [DOI: https://dx.doi.org/10.1016/j.matpr.2023.03.383]

32. Yamada, T.; Hayamizu, Y.; Yamamoto, Y.; Yomoida, Y.; Izadi-Najafabadi, A.; Futaba, N.; Hata, K. A stretchable carbon nanotube strain sensor for human-motion detection. Nat. Nanotechnol.; 2011; 6, pp. 296-301. [DOI: https://dx.doi.org/10.1038/nnano.2011.36] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/21441912]

33. Omprakash, P.; Kuruveri, U.B.; Panemangalore, B. Carbon and Metallic-based Nanomaterials for Strain Sensors—A Review. Curr. Nanomater.; 2021; 6, pp. 172-184. [DOI: https://dx.doi.org/10.2174/2405461506666210112151221]

34. Nag, A.; Alahi, M.E.E.; Mukhopadhyay, S.C.; Liu, Z. Multi-Walled Carbon Nanotubes-Based Sensors for Strain Sensing Applications. Sensors; 2021; 21, 1261. [DOI: https://dx.doi.org/10.3390/s21041261] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/33578782]

35. Nag, A.; Feng, S.; Mukhopadhyay, S.; Kosel, J.; Inglis, D. 3D printed mould-based graphite/PDMS sensor for low-force applications. Sens. Actuators A Phys.; 2018; 280, pp. 525-534. [DOI: https://dx.doi.org/10.1016/j.sna.2018.08.028]

36. Pástor, M.; Trebuňa, F.; Lengvarský, P.; Bocko, J. Possibility of Using of Tensometry in Deformation Analysis in Areas With Sudden Change of Geometry. Am. J. Mech. Eng.; 2016; 4, pp. 363-367. [DOI: https://dx.doi.org/10.12691/ajme-4-7-23]

37. Lin, H.; Li, H.; Shao, G.; Ye, Y.; Yang, Y. Zero-point fault detection of load cells in truck scale based on recursive principal component analysis and comprehensive evaluation method. Measurement; 2020; 159, 107706. [DOI: https://dx.doi.org/10.1016/j.measurement.2020.107706]

38. Ayu, H.D.; Jufriadi, A.; Pranata, K.B.; Endarko, E.; Muntini, M.S. Strain gauge sensor of mass measurement using a brass cantilever. J. Neutrino J. Fis. Dan Apl.; 2017; 9, pp. 52-59. [DOI: https://dx.doi.org/10.18860/neu.v9i2.4138]

39. Al-Dahiree, O.S.; Tokhi, M.O.; Hadi, N.H.; Hmoad, N.R.; Ghazilla, R.A.R.; Yap, H.J.; Albaadani, E.A. Design and Shape Optimization of Strain Gauge Load Cell for Axial Force Measurement for Test Benches. Sensors; 2022; 22, 7508. [DOI: https://dx.doi.org/10.3390/s22197508] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/36236608]

40. Sugishita, J.; McKenzie, M.; Torres, L.G.; Seddon, P.J. Automated techniques for measuring meal size in great albatrosses. N. Z. J. Ecol.; 2017; 41, pp. 120-125. [DOI: https://dx.doi.org/10.20417/nzjecol.41.6]

41. Petrone, N.; Capuzzo, M.; Paoli, E.; Biliato, N. The Measurement of Aerodynamic Loads using Dynamometric Load Cells. Meas. Test.; 2004; 4, pp. 56-59. [DOI: https://dx.doi.org/10.1007/BF03246829]

42. Kamatchi, M.; Mendoza, C.; Venusamy, K. Design and Implementation of PLC based Smart Coffee Maker. IOP Conf. Ser. Earth Environ. Sci.; 2022; 1055, 012011. [DOI: https://dx.doi.org/10.1088/1755-1315/1055/1/012011]

43. Rogacheva, N.; Sidorov, V.; Zheglova, Y. Piezoelectric Gauge of Small Dynamic Bending Strains. Buildings; 2024; 14, 2447. [DOI: https://dx.doi.org/10.3390/buildings14082447]

44. Anaf, W.; Cabal, A.; Robbe, M.; Schalm, O. Real-Time Wood Behaviour: The Use of Strain Gauges for Preventive Conservation Applications. Sensors; 2020; 20, 305. [DOI: https://dx.doi.org/10.3390/s20010305] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/31935854]

45. Gaute-Alonso, A.; Garcia-Sanchez, D.; Ramos-Gutierrez, Ó.R.; Ntertimanis, V. Enhancing stress measurements accuracy control in the construction of long-span bridges. Sci. Rep.; 2024; 14, 10961. [DOI: https://dx.doi.org/10.1038/s41598-024-61873-y] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/38745071]

46. Freddi, A.; Olmi, G.; Cristofolini, L. Introduction to the application of strain gages. Experimental Stress Analysis for Materials and Structures; Springer International Publishing: Berlin/Heidelberg, Germany, 2015; Volume 4, pp. 23-100. [DOI: https://dx.doi.org/10.1007/978-3-319-06086-6_2]

47. Liu, B.; Pang, J.; Tu, X.; Zhou, Z. Three components strain-gauge type aircraft surface friction resistance sensor: Design, manufacturing, and calibration. Measurement; 2023; 218, 113165. [DOI: https://dx.doi.org/10.1016/j.measurement.2023.113165]

48. Dos Santos, F.L.M.; Peeters, B. On the use of strain sensor technologies for strain modal analysis: Case studies in aeronautical applications. Rev. Sci. Instrum.; 2016; 87, 102506. [DOI: https://dx.doi.org/10.1063/1.4965814] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/27802749]

49. Xia, Y.; Zhu, J.; Wang, K.; Zhou, Q. Design and verification of a strain gauge based load sensor for medium-speed dynamic tests with a hydraulic test machine. Int. J. Impact Eng.; 2016; 88, pp. 139-152. [DOI: https://dx.doi.org/10.1016/j.ijimpeng.2015.10.004]

50. Schäfer, A. New strain gauge-based torque reference chain offering smallest measurement uncertainties. Proceedings of the 19th International Congress of Metrology; Paris, France, 24–26 September 2019; 27008. [DOI: https://dx.doi.org/10.1051/metrology/201927008]

51. Shi, L.; Feng, J.; Zhu, Y.; Huang, F.; Aw, K. A review of flexible strain sensors for walking gait monitoring. Sens. Actuators A Phys.; 2024; 377, 115730. [DOI: https://dx.doi.org/10.1016/j.sna.2024.115730]

52. Yadav, A.; Yadav, N.; Wu, Y.; RamaKrishna, S.; Hongyu, Z. Wearable strain sensors: State-of-the-art and future applications. Mater. Adv.; 2023; 4, 1444. [DOI: https://dx.doi.org/10.1039/D2MA00818A]

53. Cordey, J.; Gautier, E. Strain gauges used in the mechanical testing of bones. Part I: Theoretical and technical aspects. Injury; 1999; 30, pp. A7-A13. [DOI: https://dx.doi.org/10.1016/S0020-1383(99)00120-5] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/10645363]

54. Zadro, M.; Braitenberg, C. Measurements and interpretations of tilt–strain gauges in seismically active areas. Earth-Sci. Rev.; 1999; 47, pp. 151-187. [DOI: https://dx.doi.org/10.1016/S0012-8252(99)00028-8]

55. Sun, C.; Tang, G.; Chapman, S.; Zhang, H.; Fortin, J.; Wang, S.; Pan, D.; Yue, J. A numerical assessment of local strain measurements on the attenuation and modulus dispersion in rocks with fluid heterogeneities. Geophys. J. Int.; 2023; 235, pp. 951-969. [DOI: https://dx.doi.org/10.1093/gji/ggad289]

56. Robinson, G.M. Finite element modelling of load cell hysteresis. Measurement; 1997; 20, pp. 103-107. [DOI: https://dx.doi.org/10.1016/S0263-2241(97)00021-3]

57. Rogacheva, N.N. The Theory of Piezoelectric Shells and Plates; CRC Press: Boca Raton, FL, USA, Ann Arbor, MI, USA, London, UK, Tokyo, Japan, 1994; 260p.

58. Swainger, K.H. Electrical Resistance Wire Strain-Gauges to Measure Large Strains. Nature; 1947; 159, pp. 61-62. [DOI: https://dx.doi.org/10.1038/159061c0]

59. Shepherd, R. Strain measurement using vibrating-wire gages. Exp. Mech.; 1964; 4, pp. 244-248. [DOI: https://dx.doi.org/10.1007/BF02322958]

60. Sinha, N.K. Use of foil strain gauges in ice over a wide loading rate. Cold Reg. Sci. Technol.; 1989; 16, pp. 145-158. [DOI: https://dx.doi.org/10.1016/0165-232X(89)90015-3]

61. Tuttle, M.E.; Brinson, H.F. Resistance-foil strain-gage technology as applied to composite materials. Exp. Mech.; 1984; 24, pp. 54-65. [DOI: https://dx.doi.org/10.1007/BF02323207]

62. Kular, G.S. Use of foil strain gage at high hydrostatic pressure. Exp. Mech.; 1972; 12, pp. 311-316. [DOI: https://dx.doi.org/10.1007/BF02320486]

63. Manshin, Y.P.; Manshina, E.Y.; Geue, M. About the dynamic error of strain gauge torque measuring devices. J. Phys. Conf. Ser.; 2021; 2131, 052041. [DOI: https://dx.doi.org/10.1088/1742-6596/2131/5/052041]

64. Ort, W. New Developments in Foil Strain-gage Transducers. Exp. Tech.; 1983; 7, pp. 19-23. [DOI: https://dx.doi.org/10.1111/j.1747-1567.1983.tb01796.x]

65. Qiu, H.; Yang, Y.; Sun, P.; Chao, G.; Wu, Y.; Chen, Y. Hypersonic aerodynamic force balance using temperature compensated semiconductor strain gauges. Adv. Aerodyn.; 2023; 5, 29. [DOI: https://dx.doi.org/10.1186/s42774-023-00160-2]

66. Cui, Y.; Li, X.; Zhang, T.; Ding, W.; Yin, J. Development of High-Temperature Wire-Grid Thin Film Strain Gauges. Sensors; 2022; 22, 7595. [DOI: https://dx.doi.org/10.3390/s22197595]

67. Wu, C.; Lin, F.; Fu, Y.; Zeng, Y.; Chen, G.; Xu, L.; Pan, X.; Chen, Q.; Sun, D.; Hai, Z. Multilayer co-sintered Pt thin-film strain gauge for high-temperature applications. Surf. Coat. Technol.; 2023; 459, 129380. [DOI: https://dx.doi.org/10.1016/j.surfcoat.2023.129380]

68. Lei, J.F.; Will, H.A. Thin-film thermocouples and strain-gauge technologies for engine applications. Sens. Actuators A; 1998; 65, pp. 187-193. [DOI: https://dx.doi.org/10.1016/S0924-4247(97)01683-X]

69. Pan, X.; Lin, F.; Wu, C.; Zeng, Y.; Chen, G.; Chen, Q.; Sun, D.; Hai, Z. Additive-Manufactured Platinum Thin-Film Strain Gauges for Structural Microstrain Testing at Elevated Temperatures. Micromachines; 2022; 13, 1472. [DOI: https://dx.doi.org/10.3390/mi13091472] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/36144095]

70. Hempel, M.; Nezich, D.; Kong, J. Hofmann A Novel Class of Strain Gauges Based on Layered Percolative Films of 2D Materials. Nano Lett.; 2012; 12, pp. 5714-5718. [DOI: https://dx.doi.org/10.1021/nl302959a] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/23045955]

71. Zhao, Y.; Liu, J.; Ying, Y.; Chen, H.; Wang, W.; Zhang, S.; Hai, Z. Temperature self-compensation thin film strain gauges based on nano-SiO2/AgNP composites. J. Mater. Chem. C; 2024; 12, pp. 12491-12498. [DOI: https://dx.doi.org/10.1039/D4TC01645A]

72. Shu, J.; Yang, R.; Chang, Y.; Guo, X.; Yang, X. A flexible metal thin film strain sensor with micro/nano structure for large deformation and high sensitivity strain measurement. J. Alloys Compd.; 2021; 879, 160466. [DOI: https://dx.doi.org/10.1016/j.jallcom.2021.160466]

73. Kayser, P.; Godefroy, J.C.; Leca, L. High-temperature thin-film strain gauges. Sens. Actutors A Phys.; 1993; 37–38, pp. 328-332. [DOI: https://dx.doi.org/10.1016/0924-4247(93)80055-L]

74. Bosque, A.; Sánchez-Romate, X.; Sánchez, M.; Ureña, A. Toward flexible piezoresistive strain sensors based on polymer nanocomposites: A review on fundamentals, performance, and applications. Nanotechnology; 2024; 35, 292003. [DOI: https://dx.doi.org/10.1088/1361-6528/ad3e87]

75. Haghgoo, M.; Ansari, R.; Hassanzadeh-Aghdam, M.K.; Tian, L.; Nankali, M. Analytical formulation of the piezoresistive behavior of carbon nanotube polymer nanocomposites: The effect of temperature on strain sensing performance. Compos. Part A Appl. Sci. Manuf.; 2022; 163, 107244. [DOI: https://dx.doi.org/10.1016/j.compositesa.2022.107244]

76. Heckmann, U.; Bandorf, R.; Gerdes, H.; Lübke, M.; Schnabel, S.; Bräuer, G. New materials for sputtered strain gauges. Procedia Chem.; 2009; 1, pp. 64-67. [DOI: https://dx.doi.org/10.1016/j.proche.2009.07.016]

77. Zarfl, C.; Schmid, P.; Balogh, G.; Schmid, U. Electro-mechanical properties and oxidation behaviour of TiAlNxOy thin films at high temperatures. Sens. Actuators A Phys.; 2015; 226, pp. 143-148. [DOI: https://dx.doi.org/10.1016/j.sna.2015.02.026]

78. Schmid, P.; Triendl, F.; Zarfl, C.; Schwarz, S.; Artner, W.; Schneider, M.; Schmid, U. Influence of the AlN/Pt-ratio on the electromechanical properties of multilayered AlN/Pt thin film strain gauges at high temperatures. Sens. Actuators A Phys.; 2020; 302, 111805. [DOI: https://dx.doi.org/10.1016/j.sna.2019.111805]

79. Schmid-Engel, H.; Uhlig, S.; Werner, U.; Schultes, G. Strain sensitive Pt-SiO₂ nano-cermet thin films for high temperature pressure and force sensors. Sens. Actuators A Phys.; 2014; 206, pp. 17-21. [DOI: https://dx.doi.org/10.1016/j.sna.2013.11.021]

80. Kalpana, H.M.; Prasad, V.S. Development of the invar36 thin film strain gauge sensor for strain measurement. Meas. Sci. Technol.; 2014; 25, 065102. [DOI: https://dx.doi.org/10.1088/0957-0233/25/6/065102]

81. Fricke, S.; Friedberger, A.; Seidel, H.; Schmid, U. A robust pressure sensor for harsh environmental applications. Sens. Actuators A Phys.; 2012; 184, pp. 16-21. [DOI: https://dx.doi.org/10.1016/j.sna.2012.05.043]

82. Yang, Y.; Shi, L.; Cao, Z.; Wang, R.; Sun, J. Strain sensors with a high sensitivity and a wide sensing range based on a Ti₃C₂Tx (MXene) nanoparticle–nanosheet hybrid network. Adv. Funct. Mater.; 2019; 29, 1807882. [DOI: https://dx.doi.org/10.1002/adfm.201807882]

83. Yang, K.; Yin, F.; Xia, D.; Peng, H.; Yang, J.; Yuan, W. A highly flexible and multifunctional strain sensor based on a networkstructured MXene/polyurethane mat with ultra-high sensitivity and a broad sensing range. Nanoscale; 2019; 11, pp. 9949-9957. [DOI: https://dx.doi.org/10.1039/C9NR00488B]

84. Li, T.; Li, J.; Zhong, A.; Han, F.; Sun, R.; Wong, C.-P.; Niu, F.; Zhang, G.; Jin, Y. A flexible strain sensor based on CNTs/PDMS microspheres for human motion detection. Sens. Actuators A Phys.; 2020; 306, 111959. [DOI: https://dx.doi.org/10.1016/j.sna.2020.111959]

85. Fu, X.; Ramos, M.; Al-Jumaily, A.M.; Meshkinzar, A.; Huang, X. Stretchable strain sensor facilely fabricated based on multi-wall carbon nanotube composites with excellent performance. J. Mater. Sci.; 2019; 54, pp. 2170-2180. [DOI: https://dx.doi.org/10.1007/s10853-018-2954-4]

86. Lu, S.; Ma, J.; Ma, K.; Wang, X.; Wang, S.; Yang, X.; Tang, H. Highly sensitive graphene platelets and multi-walled carbon nanotube-based flexible strain sensor for monitoring human joint bending. Appl. Phys. A; 2019; 125, 471. [DOI: https://dx.doi.org/10.1007/s00339-019-2765-8]

87. Abshirini, M.; Charara, M.; Liu, Y.; Saha, M.; Altan, M.C. 3D printing of highly stretchable strain sensors based on carbon nanotube nanocomposites. Adv. Eng. Mater.; 2018; 20, 1800425. [DOI: https://dx.doi.org/10.1002/adem.201800425]

88. Alamusi,; Hu, N.; Fukunaga, H.; Atobe, S.; Liu, Y.; Li, J. Piezoresistive Strain Sensors Made from Carbon Nanotubes Based Polymer Nanocomposites. Sensors; 2011; 11, pp. 10691-10723. [DOI: https://dx.doi.org/10.3390/s111110691] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/22346667]

89. Kumar, S.; Gupta, T.K.; Varadarajan, K. Strong, stretchable and ultrasensitive MWCNT/TPU nanocomposites for piezoresistive strain sensing. Compos. Part. B Eng.; 2019; 177, 107285. [DOI: https://dx.doi.org/10.1016/j.compositesb.2019.107285]

90. Giffney, T.; Bejanin, E.; Kurian, A.S.; Travas-Sejdic, J.; Aw, K. Highly stretchable printed strain sensors using multi-walled carbon nanotube/silicone rubber composites. Sens. Actuators A Phys.; 2017; 259, pp. 44-49. [DOI: https://dx.doi.org/10.1016/j.sna.2017.03.005]

91. Li, X.; Wang, R.; Wang, L.; Li, A.; Tang, X.; Choi, J.; Zhang, P.; Jin, M.L.; Joo, S.W. Scalable fabrication of carbon materials based silicon rubber for highly stretchable e-textile sensor. Nanotechnol. Rev.; 2020; 9, pp. 1183-1191. [DOI: https://dx.doi.org/10.1515/ntrev-2020-0088]

92. Tadakaluru, S.; Thongsuwan, W.; Singjai, P. Stretchable and flexible high-strain sensors made using carbon nanotubes and graphite films on natural rubber. Sensors; 2014; 14, pp. 868-876. [DOI: https://dx.doi.org/10.3390/s140100868]

93. He, Z.; Zhou, G.; Byun, J.-H.; Lee, S.-K.; Um, M.-K.; Park, B.; Kim, T.; Lee, S.B.; Chou, T.-W. Highly stretchable multi-walled carbon nanotube/thermoplastic polyurethane composite fibers for ultrasensitive, wearable strain sensors. Nanoscale; 2019; 11, pp. 5884-5890. [DOI: https://dx.doi.org/10.1039/C9NR01005J]

94. Abshirini, M.; Charara, M.; Marashizadeh, P.; Saha, M.C.; Altan, M.C.; Liu, Y. Functional nanocomposites for 3D printing of stretchable and wearable sensors. Appl. Nanosci.; 2019; 9, pp. 2071-2083. [DOI: https://dx.doi.org/10.1007/s13204-019-01032-2]

95. Sahatiya, P.; Badhulika, S. Eraser-based eco-friendly fabrication of a skin-like large-area matrix of flexible carbon nanotube strain and pressure sensors. Nanotechnology; 2017; 28, 095501. [DOI: https://dx.doi.org/10.1088/1361-6528/aa5845]

96. Zhang, S.; Wang, H.; Wen, L.; Zhu, K.; Liao, Z.; Deng, Y.; Zhang, M. Reinforced standing multi-walled carbon nanotube film for stretchable strain sensor. Proceedings of the 2017 IEEE 17th International Conference on Nanotechnology (IEEE-NANO); Pittsburgh, PA, USA, 25–27 July 2017; pp. 474-478.

97. Huang, K.; Ning, H.; Hu, N.; Liu, F.; Wu, X.; Wang, S.; Liu, Y.; Zou, R.; Yuan, W.; Wu, L. Ultrasensitive MWCNT/PDMS composite strain sensor fabricated by laser ablation process. Compos. Sci. Technol.; 2020; 192, 108105. [DOI: https://dx.doi.org/10.1016/j.compscitech.2020.108105]

98. Reverter, F. A Tutorial on Mechanical Sensors in the 70th Anniversary of the Piezoresistive Effect. Sensors; 2024; 24, 3690. [DOI: https://dx.doi.org/10.3390/s24113690]

99. Kouediatouka, A.N.; Liu, Q.; Mawignon, F.J.; Wang, W.; Wang, J.; Ruan, C.; Yeo, K.F.H.; Dong, G. Sensing characterization of an amorphous PDMS/Ecoflex blend composites with an improved interfacial bonding and rubbing performance. Appl. Surf. Sci.; 2023; 635, 157675. [DOI: https://dx.doi.org/10.1016/j.apsusc.2023.157675]

100. Ke, K.; Yue, L.; Shao, H.; Yang, M.-B.; Yang, W.; Manas-Zloczower, I. Boosting electrical and piezoresistive properties of polymer nanocomposites via hybrid carbon fillers: A review. Carbon; 2021; 173, pp. 1020-1040. [DOI: https://dx.doi.org/10.1016/j.carbon.2020.11.070]

101. Roy, A.; Gupta, A.; Haque, B.; Qureshi, A.A.; Verma, D.; Sharma, K.; Lee, S.F.; Hee, C.W.; Roy, A.; Verma, R. An updated review on carbon nanomaterials: Types, synthesis, functionalization and applications, degradation and toxicity. Green Process. Synth.; 2024; 13, 2020150. [DOI: https://dx.doi.org/10.1515/gps-2024-0150]

102. Liu, W.; Xue, C.; Long, X.; Ren, Y.; Chen, Z.; Zhang, W. Highly flexible and multifunctional CNTs/TPU fiber strain sensor formed in one-step via wet spinning. J. Alloys Compd.; 2023; 948, 169641. [DOI: https://dx.doi.org/10.1016/j.jallcom.2023.169641]

103. Abot, J.L.; Góngora-Rubio, M.R.; Anike, J.C.; César, Y.; Kiyono, C.Y.; Mello, L.A.; Cardoso, V.F.; Rosa, R.L.; Kuebler, D.A.; Brodeur, G.E. et al. Foil Strain Gauges Using Piezoresistive Carbon Nanotube Yarn: Fabrication and Calibration. Sensors; 2018; 18, 464. [DOI: https://dx.doi.org/10.3390/s18020464]

104. Arana, G.; Mora, A.; Pérez, I.; Avilés, F. Design and analysis of a carbon nanotube-based strain gauge via multiscale modeling. Meccanica; 2023; 58, pp. 1717-1732. [DOI: https://dx.doi.org/10.1007/s11012-023-01689-8]

105. Santos, A.R.; Viana, J.C. The Development of a Flexible Humidity Sensor Using MWCNT/PVA Thin Films. Nanomaterials; 2024; 14, 1653. [DOI: https://dx.doi.org/10.3390/nano14201653] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/39452989]

106. Chumak, M.A.; Shchegolkov, A.V.; Popov, E.O.; Filippov, S.V.; Kolosko, A.G.; Shchegolkov, A.V.; Babaev, A.A. Investigation of Field Emission Properties of Carbon Nanotube Arrays of Different Morphologies. Nanomaterials; 2024; 14, 763. [DOI: https://dx.doi.org/10.3390/nano14090763]

107. Georgousis, G.; Pandis, C.; Kalamiotis, A.; Georgiopoulos, P.; Kyritsis, A.; Kontou, E.; Pissis, P.; Micusik, M.; Czanikova, K.; Kulicek, J. et al. Strain sensing in polymer/carbon nanotube composites by electrical resistance measurement. Compos. Part B Eng.; 2015; 68, pp. 162-169. [DOI: https://dx.doi.org/10.1016/j.compositesb.2014.08.027]

108. Salaeh, S.; Das, A.; Stöckelhuber, K.W.; Wießner, S. Fabrication of a strain sensor from a thermoplastic vulcanizate with an embedded interconnected conducting filler network. Compos. Part A Appl. Sci. Manuf.; 2020; 130, 105763. [DOI: https://dx.doi.org/10.1016/j.compositesa.2020.105763]

109. Tang, Z.; Huang, Q.; Liu, Y.; Chen, Y.; Guo, B.; Zhang, L. Uniaxial Stretching-Induced Alignment of Carbon Nanotubes in Cross-Linked Elastomer Enabled by Dynamic Cross-Link Reshuffling. ACS Macro Lett.; 2019; 8, pp. 1575-1581. [DOI: https://dx.doi.org/10.1021/acsmacrolett.9b00836] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/35619384]

110. Tran, V.V.; Lee, K.; Nguyen, T.N.; Lee, D. Recent Advances and Progress of Conducting Polymer-Based Hydrogels in Strain Sensor Applications. Gels; 2023; 9, 12. [DOI: https://dx.doi.org/10.3390/gels9010012] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/36661780]

111. Lin, L.; Park, P.; Kim, Y.; Bae, M.; Lee, J.; Zhang, W.; Gao, J.; Paek, S.H.; Piao, Y. Wearable and stretchable conductive polymer composites for strain sensors: How to design a superior one?. Nano Mater. Sci.; 2023; 5, pp. 392-403. [DOI: https://dx.doi.org/10.1016/j.nanoms.2022.08.003]

112. Avilés, F. Thermoresistivity of Carbon Nanostructures and their Polymeric Nanocomposites. Adv. Mater. Interfaces.; 2023; 10, 2300218. [DOI: https://dx.doi.org/10.1002/admi.202300218]

113. Peng, K.; Yu, T.; Wu, P.; Chen, M. Piezoresistive Porous Composites with Triply Periodic Minimal Surface Structures Prepared by Self-Resistance Electric Heating and 3D Printing. Sensors; 2024; 24, 2184. [DOI: https://dx.doi.org/10.3390/s24072184] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/38610395]

114. Siva Yellampalli, S. Carbon Nanotubes—Polymer Nanocomposites; Lerche&Johmson: Rijeka, Croatia, 2010; 396.

115. Gong, S.; Zhu, Z.H.; Li, Z. Electron tunnelling and hopping effects on the temperature coefficient of resistance of carbon nanotube/polymer nanocomposites. Phys. Chem. Chem. Phys.; 2017; 19, pp. 5113-5120. [DOI: https://dx.doi.org/10.1039/C6CP08115K]

116. Neilson, J.; Cataldi, P.; Derby, B. Graphene-Based Transparent Flexible Strain Gauges with Tunable Sensitivity and Strain Range. ACS Appl. Nano Mater.; 2023; 6, pp. 21763-21774. [DOI: https://dx.doi.org/10.1021/acsanm.3c03967]

117. Burzhuev, S.; Dâna, A.; Ortac, B. Laser synthesized gold nanoparticles for high sensitive strain gauges. Sens. Actuators A Phys.; 2013; 203, pp. 131-136. [DOI: https://dx.doi.org/10.1016/j.sna.2013.08.034]

118. Puyoo, E.; Malhaire, C.; Thomas, D.; Rafaël, R.; R’Mili, M.; Malchère, A.; Roiban, L.; Koneti, S.; Bugnet, M.; Sabac, A. et al. Metallic nanoparticle-based strain sensors elaborated by atomic layer deposition. Appl. Phys. Lett.; 2017; 110, 123103. [DOI: https://dx.doi.org/10.1063/1.4978778]

119. Zhang, S.; Cai, L.; Li, W.; Miao, J.; Wang, T.; Yeom, J.; Sepúlveda, N.; Wang, C. Fully Printed Silver-Nanoparticl-Based Strain Gauges with Record High Sensitivity. Adv. Electron. Mater.; 2017; 3, 1700067. [DOI: https://dx.doi.org/10.1002/aelm.201700067]

120. Xiang, D.; Zhang, X.; Han, Z.; Zhang, Z.; Zhou, Z.; Harkin-Jones, E.; Zhang, J.; Luo, X.; Wang, P.; Zhao, C. et al. 3D printed high-performance flexible strain sensors based on carbon nanotube and graphene nanoplatelet filled polymer composites. J. Mater. Sci.; 2020; 55, pp. 15769-15786. [DOI: https://dx.doi.org/10.1007/s10853-020-05137-w]

121. He, Z.; Byun, J.-H.; Zhou, G.; Park, B.-J.; Kim, T.-H.; Lee, S.-B.; Yi, J.-W.; Um, M.-K.; Chou, T.-W. Effect of MWCNT content on the mechanical and strain-sensing performance of Thermoplastic Polyurethane composite fibers. Carbon; 2019; 146, pp. 701-708. [DOI: https://dx.doi.org/10.1016/j.carbon.2019.02.060]

122. Xu, Y.; Xie, X.; Huang, H.; Wang, Y.; Yu, J.; Hu, Z. Encapsulated core–sheath carbon nanotube–graphene/polyurethane composite fiber for highly stable, stretchable, and sensitive strain sensor. J. Mater. Sci.; 2020; 56, pp. 2296-2310. [DOI: https://dx.doi.org/10.1007/s10853-020-05394-9]

123. Gul, J.Z.; Sajid, M.; Choi, K.H. 3D printed highly flexible strain sensor based on TPU–graphene composite for feedback from high speed robotic applications. J. Mater. Chem. C.; 2019; 7, pp. 4692-4701. [DOI: https://dx.doi.org/10.1039/C8TC03423K]

124. Gao, J.; Li, B.; Huang, X.; Wang, L.; Lin, L.; Wang, H.; Xue, H. Electrically conductive and fluorine free superhydrophobic strain sensors based on SiO₂/graphenedecorated electrospun nanofibers for human motion monitoring. Chem. Eng. J.; 2019; 373, pp. 298-306. [DOI: https://dx.doi.org/10.1016/j.cej.2019.05.045]

125. Wang, Y.; Hao, J.; Huang, Z.; Zheng, G.; Dai, K.; Liu, C.; Shen, C. Flexible electrically resistive-type strain sensors based on reduced graphene oxide-decorated electrospun polymer fibrous mats for human motion monitoring. Carbon; 2018; 126, pp. 360-371. [DOI: https://dx.doi.org/10.1016/j.carbon.2017.10.034]

126. Nag-Chowdhury, S.; Bellegou, H.; Pillin, I.; Castro, M.; Longrais, P.; Feller, J.F. Non-intrusive health monitoring of infused composites with embedded carbon quantum piezo-resistive sensors. Compos. Sci. Technol.; 2016; 123, pp. 286-294. [DOI: https://dx.doi.org/10.1016/j.compscitech.2016.01.004]

127. Ning, N.; Wang, S.; Zhang, L.; Lu, Y.; Tian, M.; Chan, T.W. Synchronously tailoring strain sensitivity and electrical stability of silicone elastomer composites by the synergistic effect of a dual conductive network. Polymers; 2016; 8, 100. [DOI: https://dx.doi.org/10.3390/polym8040100]

128. Madhavan, R. Nanocrack-based ultrasensitive wearable and skin-mountable strain sensors for human motion detection. Mater. Adv.; 2022; 3, pp. 8665-8676. [DOI: https://dx.doi.org/10.1039/D2MA00897A]

129. Wang, X.; Li, H.; Wang, T.; Niu, X.; Wang, Y.; Xu, S.; Jiang, Y.; Chen, L.; Liu, H. Flexible and high-performance piezoresistive strain sensors based on multi-walled carbon nanotubes@ polyurethane foam. RSC Adv.; 2022; 12, pp. 14190-14196. [DOI: https://dx.doi.org/10.1039/D2RA01291J]

130. Knite, M.R.; Tupureina, V.; Fuith, A.; Zavickis, J.; Teteris, V. Polyisoprene–multi-wall carbon nanotube composites for sensing strain. Mater. Sci. Eng. C; 2007; 27, pp. 1125-1128. [DOI: https://dx.doi.org/10.1016/j.msec.2006.08.016]

131. Xiang, D.; Zhang, X.; Li, Y.; Harkin-Jones, E.; Zheng, Y.; Wang, L.; Zhao, C.; Wang, P. Enhanced performance of 3D printed highly elastic strain sensors of carbon nanotube/thermoplastic polyurethane nanocomposites via non-covalent interactions. Compos. Part B Eng.; 2019; 176, pp. 1359-1368. [DOI: https://dx.doi.org/10.1016/j.compositesb.2019.107250]

132. Simić, M. Microcontroller-based Readout of Resistive Sensors. IFAC-PapersOnLine; 2022; 55, pp. 242-247. [DOI: https://dx.doi.org/10.1016/j.ifacol.2022.06.040]

133. Reverter, F.; Jordana, J.; Gasulla, M.; Pallàs-Areny, R. Accuracy and resolution of direct resistive sensor-tomicrocontroller interfaces. Sens. Actuators A Phys.; 2005; 121, pp. 78-87. [DOI: https://dx.doi.org/10.1016/j.sna.2005.01.010]

134. Ferran, R. The Art of Directly Interfacing Sensors to Microcontrollers. J. Low Power Electron. Appl.; 2012; 2, pp. 265-281. [DOI: https://dx.doi.org/10.3390/jlpea2040265]

135. Yi, W.; Wang, Y.; Wang, G.; Tao, X. Investigation of carbon black/silicone elastomer/dimethylsilicone oil composites for flexible strain sensors. Polym. Test.; 2012; 31, pp. 677-684. [DOI: https://dx.doi.org/10.1016/j.polymertesting.2012.03.006]

136. Yang, S.; Lu, N. Gauge Factor and Stretchability of Silicon-on-Polymer Strain Gauges. Sensors; 2013; 13, pp. 8577-8594. [DOI: https://dx.doi.org/10.3390/s130708577] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/23881128]

137. Kang, I.; Schulz, M.J.; Kim, J.H.; Shanov, V.; Shi, D. A carbon nanotube strain sensor for structural health monitoring. Smart Mater. Struct.; 2006; 15, 737. [DOI: https://dx.doi.org/10.1088/0964-1726/15/3/009]

138. Loh, K.J.; Kim, J.; Lynch, J.P.; Kam, N.W.S.; Kotov, N.A. Multifunctional layer-by-layer carbon nanotube–polyelectrolyte thin films for strain and corrosion sensing. Smart Mater. Struct.; 2007; 16, 429. [DOI: https://dx.doi.org/10.1088/0964-1726/16/2/022]

139. Zhang, C.; Zhang, X.; Qi, X.; Liu, Y.; Li, N.; Zeng, F.; Jiang, S.; Ding, J. Polymer-based strain sensors: Review. J. Mater. Sci. Mater. Electron.; 2024; 35, 1166. [DOI: https://dx.doi.org/10.1007/s10854-024-12923-8]

140. Ramírez, J.; Urbina, A.D.; Kleinschmidt, A.T.; Finn, M.; Edmunds, S.J.; Guillermo, L.; Esparza, G.L.; Lipomi, D.J. Exploring the Limits of Sensitivity for Strain Gauges of Graphene and Hexagonal Boron Nitride Decorated with Metallic Nanoislands. Nanoscale; 2020; 12, pp. 11209-11221. [DOI: https://dx.doi.org/10.1039/D0NR02270E]

141. Mora, A.; Verma, P.; Kumar, S. Electrical conductivity of CNT/polymer composites: 3D printing, measurements and modeling. Compos. Part B Eng.; 2020; 183, 107600. [DOI: https://dx.doi.org/10.1016/j.compositesb.2019.107600]

142. Osman, A.; JLu, J. 3D printing of polymer composites to fabricate wearable sensors: A comprehensive review. Mater. Sci. Eng. R. Rep.; 2023; 154, 100734. [DOI: https://dx.doi.org/10.1016/j.mser.2023.100734]

143. Chen, J.; Yu, Q.; Cui, X.; Dong, M.; Zhang, J.; Wang, C.; Fan, J.; Zhu, Y.; Guo, Z. An overview of stretchable strain sensors from conductive polymer nanocomposites. J. Mater. Chem. C; 2019; 7, pp. 11710-11730. [DOI: https://dx.doi.org/10.1039/C9TC03655E]

144. Kablov, E.N.; Sivakov, D.V.; Gulyaev, I.N.; Sorokin, K.V.; Fedotov, M.Y.; Dianov, E.M.; Vasil’ev, S.A.; Medvedkov, O.I. Application of optical fiber as strain gauges in polymer composite materials. Polym. Sci. Ser. D; 2011; 4, pp. 246-251. [DOI: https://dx.doi.org/10.1134/S1995421211030063]

145. Xie, B.; Chen, X.; Ding, M.; Zhou, G.; Zhao, X. Design and development of a new strain measuring method based on smartphone and machine vision. Measurement; 2021; 182, 109724. [DOI: https://dx.doi.org/10.1016/j.measurement.2021.109724]

146. Li, W.H.; Zhang, X.Z.; Du, H. Magnetorheological elastomers and their applications. Advances in Elastomers I: Blends and Interpenetrating Networks; Visakh, P.M.; Thomas, S.; Chandra, A.K.; Mathew, A.P. Springer: Berlin, Germany, 2013; pp. 357-374.

147. Wang, X.; Lim, E.G.; Hoettges, K.; Song, P. A Review of Carbon Nanotubes, Graphene and Nanodiamond Based Strain Sensor in Harsh Environments. C J. Carbon Res.; 2023; 9, 108. [DOI: https://dx.doi.org/10.3390/c9040108]

148. Bi, Z.; Liu, Y.; Krider, J.; Buckland, J.; Whiteman, A.; Beachy, D.; Smith, J. Real-time force monitoring of smart grippers for Internet of Things (IoT) applications. J. Ind. Inf. Integr.; 2018; 11, pp. 19-28. [DOI: https://dx.doi.org/10.1016/j.jii.2018.02.004]

149. Lozoya-Santos, J.D.J.; Félix-Herrán, L.C.; Tudón-Martínez, J.C.; Vargas-Martinez, A.; Ramirez-Mendoza, R.A. Design and Implementation of an IoT-Oriented Strain Smart Sensor with Exploratory Capabilities on Energy Harvesting and Magnetorheological Elastomer Transducers. Appl. Sci.; 2020; 10, 4387. [DOI: https://dx.doi.org/10.3390/app10124387]

150. Liu, L.; Wang, H.; Wang, B. The more and less of AI-assisted strain sensor. Matter; 2023; 6, pp. 653-676. [DOI: https://dx.doi.org/10.1016/j.matt.2023.01.014]

151. Gavrilenkov, S.I. A Framework for Optimal Placement of Strain Gauges on Elastic Elements of Force Sensors Using Genetic Algorithms. ITM Web Conf.; 2020; 35, 04010. [DOI: https://dx.doi.org/10.1051/itmconf/20203504010]

152. Rohrbach, C.; Lexow, J. Miniature force transducers with strain gauges. Measurement; 1986; 4, pp. 93-100. [DOI: https://dx.doi.org/10.1016/0263-2241(86)90014-X]

153. Tervo, J.; Vuorio, J.; Paro, J.; Ruusuvuori, K.; Ronkainen, H. Miniature plasma sprayed strain gauges for torque sensing. Power Metallurgy; 2014; 56, pp. 335-336. [DOI: https://dx.doi.org/10.1179/0032589913Z.000000000140]

154. Sharma, K.; Singh, T.; Sehgal, S.; Goyal, P. Design and development of strain gauge for biomedical applications: State of the art review. Innov. Emerg. Technol.; 2024; 11, 2440013. [DOI: https://dx.doi.org/10.1142/S2737599424400139]

155. Yan, J.; Chen, A.; Liu, S. Flexible sensing platform based on polymer materials for health and exercise monitoring. Alex. Eng. J.; 2024; 86, pp. 405-414. [DOI: https://dx.doi.org/10.1016/j.aej.2023.11.085]

156. Masláková, K.; Trebuňa, F.; Frankovský, P.; Binda, M. Applications of the Strain Gauge for Determination of Residual Stresses using Ring-core Method. Procedia Eng.; 2012; 48, pp. 396-401. [DOI: https://dx.doi.org/10.1016/j.proeng.2012.09.531]

157. Kumar, A.; Chaturvedi, S.K.; Chaturvedi, V.; Yadaw, R.C. Design Studies and Optimization of Position of Strain Gauge. Int. J. Sci. Eng. Res.; 2012; 3, 10.

158. Distelhoff, M.F.W.; Laker, J.; Marquis, A.J.; Nouri, J.M. The application of a strain gauge technique to the measurement of the power characteristics of five impellers. Exp. Fluids; 1995; 20, pp. 56-58. [DOI: https://dx.doi.org/10.1007/BF00190598]

159. Yokaribas, V.; Wagner, S.; Schneider, D.S.; Friebertshäuser, P.; Lemme, M.C.; Fritzen, C.-P. Strain Gauges Based on CVD Graphene Layers and Exfoliated Graphene Nanoplatelets with Enhanced Reproducibility and Scalability for Large Quantities. Sensors; 2017; 17, 2937. [DOI: https://dx.doi.org/10.3390/s17122937]

160. Baldwin, J.K.; Gullett, P.M.; Howard, I.L. Strain-Based elevation monitoring during construction of the Salesforce Tower. Eng. Struct.; 2023; 297, 116957. [DOI: https://dx.doi.org/10.1016/j.engstruct.2023.116957]

161. Koivikko, A.; Lampinen, V.; Pihlajamäki, M.; Yiannacou, K.; Sharma, V.; Sariola, V. Integrated stretchable pneumatic strain gauges for electronics-free soft robots. Commun. Eng.; 2022; 1, 14. [DOI: https://dx.doi.org/10.1038/s44172-022-00015-6]

162. Ali, I.; Shchegolkov, A.V.; Shchegolkov, A.V.; Chumak, M.A.; Agustiono, K.T.; Bin, J.A.; Imanova, G. Synthesis and characterization of MWCNTs nanocomposite for fabrication of tensometric transducers. Fuller. Nanotub. Carbon Nanostructures; 2024; pp. 1-10. [DOI: https://dx.doi.org/10.1080/1536383X.2024.2401505]

163. Yi, H.; Wang, S.; Mei, S.; Li, Z. Conductive polymer composites for resistive flexible strain sensos. Polymer; 2024; 307, 127286. [DOI: https://dx.doi.org/10.1016/j.polymer.2024.127286]

164. Li, L.; Han, L.; Hu, H.; Zhang, R. A review on polymers and their composites for flexible electronics. Mater. Adv.; 2023; 4, 726. [DOI: https://dx.doi.org/10.1039/D2MA00940D]

165. Zhao, D.; Jia, W.; Feng, X.; Yang, H.; Xie, Y.; Shang, J.; Wang, P.; Guo, Y.; Li, R.-W. Flexible Sensors Based on Conductive Polymer Composites. Sensors; 2024; 24, 4664. [DOI: https://dx.doi.org/10.3390/s24144664] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/39066060]

166. Allam, V.; Vandrangi, S.K. Carbon black and boron nitride conductive fillers dispersed porous conductive polymer composite-based piezoresistive sensor for biomedical applications. J. Mater. Sci. Mater. Electron.; 2024; 35, 2248. [DOI: https://dx.doi.org/10.1007/s10854-024-14020-2]

167. Dodo, O.J.; Raji, I.; Arny, I.J.; Myers, C.P.; Petit, L.; Walpita, K.; Dunn, D.; Thrasher, C.J.; Konkolewicz, D. Dynamic polymer nanocomposites towards strain sensors and customizable resistors. RSC Appl. Polym.; 2023; 1, 30. [DOI: https://dx.doi.org/10.1039/D3LP00012E]

168. Gong, M.; Zhang, L.; Wan, P. Polymer nanocomposite meshes for flexible electronic devices. Prog. Polym. Sci.; 2020; 107, 101279. [DOI: https://dx.doi.org/10.1016/j.progpolymsci.2020.101279]

169. Dhanasekar, S.; Stella, T.J.; Thenmozhi, A.; Bharathi, N.D.; Thiyagarajan, K.; Singh, P.; Reddy, Y.S.; Srinivas, G.; Jayakumar, M. Study of Polymer Matrix Composites for Electronics Applications. J. Nanomater.; 2022; 2022, 8605099. [DOI: https://dx.doi.org/10.1155/2022/8605099]

170. Li, J.; Xiang, D.; Su, P.; Zhao, C.; Li, H.; Li, Z.; Wang, B.; Wang, P.; Li, Y.; Wu, Y. High-performance flexible strain sensors prepared by biaxially stretching conductive polymer composites with a double-layer structure. Mater. Today Commun.; 2023; 36, 106548. [DOI: https://dx.doi.org/10.1016/j.mtcomm.2023.106548]

171. Mishra, S.; Saha, B. Graphene- polymer nanocomposite-based wearable strain sensors for physiological signal Monitoring: Recent progress and challenges. Curr. Opin. Solid State Mater. Sci.; 2024; 31, 101174. [DOI: https://dx.doi.org/10.1016/j.cossms.2024.101174]

172. Truong, T.; Kim, J. A Wearable Strain Sensor Utilizing Shape Memory Polymer/Carbon Nanotube Composites Measuring Respiration Movements. Polymers; 2024; 16, 373. [DOI: https://dx.doi.org/10.3390/polym16030373]

173. Zhao, Z.; Li, Q.; Dong, Y.; Gong, J.; Li, Z.; Zhang, J. Washable Patches with Gold Nanowires/Textiles in Wearable Sensors for Health Monitoring. ACS Appl. Mater. Interfaces; 2022; 14, pp. 18884-18900. [DOI: https://dx.doi.org/10.1021/acsami.2c01729]

174. Zhan, Z.; Sun, Q.; Tang, C.; Wu, H.; Lu, Y. Ultra-highly sensitive and self-healing flexible strain sensor with a wide measuring range based on a bilayer structure. Sens. Actuators A Phys.; 2023; 360, 114510. [DOI: https://dx.doi.org/10.1016/j.sna.2023.114510]